JPH0743039B2 - mechanical seal - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mechanical seal in which two hermetically sealed end faces are rotated in relative sliding contact with each other.

[0002]

2. Description of the Related Art In this type of mechanical seal,
From the viewpoint of sealing property and durability, one sealing end face is generally made of a carbon material and the other sealing end face is made of a cemented carbide material such as tungsten carbide.

[0003]

However, as the field of use of mechanical seals has expanded in recent years, it has been possible to seal oils of high viscosity, such as in pumps used in the petrochemical field, or under high load (PVT) conditions. Since the usage conditions thereof tend to be severe, such as the case where the above-mentioned conventional mechanical seal is used, there are many cases where the conventional mechanical seal cannot be used.

That is, when a high-viscosity oil is sealed, high heat is generated between the sealed end faces due to a large sliding resistance, and the generated heat causes the sealed end faces made of carbon to remain in a short time. Partially raised in the inside, the raised portion is destroyed and carbon is detached, or cracks occur in the raised portion even if carbon is not detached (hereinafter, such phenomenon is referred to as “blister”).
Generically). Then, if a blister occurs on the carbon seal end face, a large amount of leakage occurs between the seal end faces,
The predetermined sealing function cannot be exerted.

Therefore, it has been attempted to use mesophase carbon as a countermeasure against such blisters, but it cannot prevent blisters effectively and self-lubricates as compared with ordinary carbon. It is difficult to say that it is an effective blister measure, because it is inferior and expensive.

The present invention has been made in view of the above points, and it is possible to effectively prevent the occurrence of such a phenomenon even under the condition that blisters are likely to occur such as sealing high-viscosity oil for a long term. An object of the present invention is to provide a mechanical seal capable of exhibiting a good sealing function over the entire length.

[0007]

In order to achieve the above-mentioned object, the mechanical seal of the present invention comprises one of two sealing end faces which rotate in relative sliding contact, made of a carbon material, and the other one made of boron nitride. It is proposed that the cemented carbide material is dispersed and mixed.

A sealed end surface made of a cemented carbide material mixed with boron nitride (hereinafter referred to as "BN mixed sealed end surface").
Can be obtained, for example, by adding an appropriate amount of boron nitride to tungsten carbide powder, uniformly dispersing and mixing the mixture, press-molding this into a predetermined shape, and then sintering. The amount of boron nitride added is generally 5
It is preferably set to ˜25% by volume. In addition to tungsten carbide, titanium carbide and other cermets can be appropriately selected as the cemented carbide.

[0009]

Since boron nitride is scattered in the form of independent fine pores on the BN-blended sealing end surface, even when high-viscosity oil is sealed, these pores function as a kind of oil pocket. It functions, and the lubricating action between the sealing end faces is favorably performed and the cooling action is promoted. As a result, heat generation between the sealed end faces is suppressed as much as possible, and the blister that is thermally generated at the carbon sealed end faces is effectively prevented, and a good sealing function is exhibited for a long period of time. It

By the way, under the same finishing conditions as the conventional sealing end material made of tungsten carbide, BN
The surface roughness of the compound sealing end surface is 0.08 to 0.35 μRa due to the presence of the pores, and maintaining the surface roughness in such a range promotes the above-mentioned lubricating effect and cooling effect and provides a good seal. It is extremely important for exerting its function. That is, if the surface roughness is less than 0.08 μRa, the lubricating action and cooling action between the sealed end faces are not sufficiently performed, and conversely, if it exceeds 0.35 μRa, the sealing action due to the sliding contact of the sealed end faces is maintained. Instead, a large amount of leakage will occur. Thus, in the constituent member of the BN-blended sealing end face, since boron nitride is uniformly dispersed in the cemented carbide structure in the above-mentioned form, when the BN-blended sealing end face is mirror-finished or the opposite sealing is performed. Even if it is fit by sliding contact with the end face, the pores functioning as oil pockets do not disappear, and the surface roughness can be maintained within the above range.

In addition to the above-mentioned points, the BN-blended sealing end surface has various characteristics effective for enhancing the reliability of the mechanical seal under severe operating conditions. For example, since boron nitride is a self-lubricating substance as is well known, B made of a cemented carbide material in which it is uniformly dispersed and blended.
The N-containing hermetically sealed end face is extremely superior in self-lubricating property as compared with the hermetically sealed end face made of a usual cemented carbide material. Further, since boron nitride has excellent wear resistance and corrosion resistance as well as cemented carbides such as tungsten carbide, the addition of boron nitride may impair the characteristics of the cemented carbide itself. Absent. Further, since boron nitride is dispersed in the structure of the cemented carbide, thermal cracks are prevented in the dispersed pores, and the thermal crack resistance is significantly improved. Moreover, the stress is relieved in the dispersed boron nitride portion, the toughness is improved, and the thermal shock resistance is improved. Furthermore, since boron nitride, that is, a solid lubricant, is dispersed and mixed in the cemented carbide, the lubricant may flow out and deteriorate the characteristics of the sealing material itself, as in the case of using an oil-impregnated material. There is no.

[0012]

EXAMPLES As an example, a mechanical seal which can be mounted on a rotary shaft having a shaft diameter of 40 mm, and which has a sealing end surface made of a combination of normal carbon and tungsten carbide in which boron nitride is uniformly dispersed and mixed. Was produced. Further, as a comparative example, the mechanical seal has the same structure as the above mechanical seal, but the sealed end face material is a mechanical seal made of a combination of tungsten and carbide that does not contain normal carbon and boron nitride, and does not contain mesophase carbon and boron nitride. Each mechanical seal made with a combination of tungsten carbide was manufactured.

Then, each mechanical seal was incorporated into the rotary shaft, and the start and stop were repeated at intervals of 30 minutes under the following conditions.

Sealed fluid: C heavy oil Fluid pressure: 7 Kgf / cm ² Fluid temperature: 30 ° C. (temperature when operation is stopped) Rotation speed: 3600 rpm

As a result, in the mechanical seal of the comparative example, the fluid temperature rose to 90 ° C. during operation, blistering occurred at the time of starting and stopping twice (2 hours), and a large amount of leakage occurred. Also, with mechanical seals, the fluid temperature rises to 90 ° C during operation, and the number of starts and stops is 15 (15
Blisters occurred at the time point (h) and a large amount of leakage occurred.

On the other hand, in the mechanical seal of the embodiment,
It was confirmed that the fluid temperature rose only to 80 ° C. during operation, no large amount of leakage occurred even when the number of times of starting and stopping was 160 times (160 hours), and blister did not occur. Finally, the blister occurred when the number of times of starting and stopping was 164 times (164 hours).

From the above experimental results, it is possible to effectively prevent the occurrence of blisters even under the severe conditions as described above, by using a combination of carbon and boron carbide as a material for the sealing end face. It is understood that it is possible to exert a good sealing function for a long period of time.

As described above, ordinary carbon is sufficient as the constituent material of the carbon sealing end face, but it goes without saying that mesophase carbon may be used if necessary. Further, the mechanical seal according to the present invention can be suitably used even under the condition that the sealing fluid is not a high-viscosity fluid such as the C heavy oil described above. That is, B
The presence of pores on the N-containing sealed end face promotes the lubricating effect and the cooling effect, and effectively prevents blisters on the carbon-made sealed end face.

[0019]

As is apparent from the above description, according to the present invention, the lubrication effect and the cooling effect between the sealed end faces are promoted even under severe conditions such as when sealing high viscosity oil. As a result, it is possible to effectively prevent blisters on the carbon-sealed end face, and it is possible to exert a good sealing function for a long period of time.

Claims (1)

[Claims] 1. A mechanical seal in which one of two sealed end faces that rotate in relative sliding contact is made of a carbon material and the other is made of a cemented carbide material in which boron nitride is dispersed and mixed.